Method and a device for acquiring an image having two-dimensional spatial resolution and spectral resolution

ABSTRACT

The present disclosure relates to devices and methods for acquiring an image having two-dimensional spatial resolution and spectral resolution. An example method comprises: acquiring a frame using rows of photo-sensitive areas on a sensor surface detecting incident light from an object imaged by an optical system onto an image plane, wherein rows of photo-sensitive areas are arranged to receive different wavelengths; moving the sensor surface in a direction perpendicular to a longitudinal direction of the rows; repeating the acquiring and moving for acquiring a plurality of frames recording different spectral information for respective positions on the object; and combining information from the plurality of frames to form multiple channels of an image, wherein each channel is formed based on detected light in respective rows and represent a two-dimensional image of the object for a different wavelength.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a non-provisional patent application claimingpriority to European Patent Application No. 16179722.0, filed Jul. 15,2016, the contents of which are hereby incorporated by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to a method and a device for acquiring animage, wherein the image has two-dimensional spatial resolution andspectral resolution.

BACKGROUND

Line-scan image capturing devices are often used when an image of anobject is to be acquired with high spectral resolution. Line-scan imagecapturing devices may typically be used in remote sensing or imaging ofobjects on a conveyor belt, wherein the object moves in relation to theimage sensor.

A line-scan image capturing device may image a particular part of anobject onto a row of pixels on an image sensor. As the object is moved,the particular part of the object is imaged onto another row of pixelson the image sensor. Different rows of pixels may be sensitive todifferent wavelengths of light, such that, as the object is moved overthe sensor area, an image with high spectral and spatial resolution maybe obtained.

Using a line-scan image capturing device may be particularly useful inspecific applications, e.g. in remote sensing in light-starvedsituations, such as a camera installed in an aerial vehicle whichmonitors the ground below, and in imaging of objects on a conveyor belt.In such applications, the recording of received light in image rows maybe synchronized with movement speed of the object on the sensor surface.

Imaging of objects using a line-scan image capturing device is not veryfast, as the object needs to be moved across the sensor surface in orderfor a full spectrally resolved image to be acquired. Also, the imagingis adapted to movement of an object in relation to the image capturingdevice.

It would be desirable to extend usage of the concept of line-scanimaging to other applications.

SUMMARY

The example embodiments described herein provide a method and devicefacilitating capture of an image having two-dimensional spatialresolution and spectral resolution. The example embodiments allow foracquisition of hyperspectral images in a fast manner, using a compactcamera.

According to a first aspect of the disclosure, there is provided amethod for acquiring an image having two-dimensional spatial resolutionand spectral resolution, the method comprising: acquiring a frame usingrows of photo-sensitive areas on at least one sensor surface, which atleast one sensor surface is arranged in relation to at least one opticalsystem in an image plane defined by the at least one optical system,wherein the photo-sensitive areas are arranged to detect incident lightfrom an object imaged by the at least one optical system onto the imageplane and rows of photo-sensitive areas are arranged to receivedifferent wavelengths of light; moving the at least one sensor surfacein the image plane in a direction perpendicular to a longitudinaldirection of the rows of photo-sensitive areas; repeating the acquiringfor acquiring a plurality of frames using different positions of the atleast one sensor surface in relation to the at least one optical systemfor recording different spectral information for respective positions onthe object; and combining information from the plurality of frames toform multiple channels of an image, wherein each channel is formed basedon detected light in respective rows of photo-sensitive areas andrepresent a two-dimensional image of the object for a differentwavelength.

According to a second aspect of the disclosure, there is provided adevice for acquiring an image having two-dimensional spatial resolutionand spectral resolution, the device comprising: at least one opticalsystem, wherein each optical system of the at least one optical systemis configured to define an image plane and direct light from an objecttowards the image plane; at least one sensor surface comprisingphoto-sensitive areas for detecting incident light, wherein rows ofphoto-sensitive areas are arranged to receive different wavelengths oflight; a translator, wherein the translator is arranged to carry the atleast one sensor surface for moving the at least one sensor surface inthe image plane in a direction perpendicular to a longitudinal directionof the rows of photo-sensitive areas; and the translator being arrangedto be controlled for synchronizing movement of the sensor surface withacquiring of a plurality of frames, wherein a frame in the plurality offrames is acquired by arranging a sub-set of the rows of photo-sensitiveareas in the image plane to receive incident light from the at least oneoptical system.

According to the disclosure, at least one sensor surface may betranslated in relation to at least one optical system, wherein eachoptical system of the at least one optical system defines an imageplane. For brevity and simplicity, the relation between the at least onesensor surface and the at least one optical system will mainly be madein relation to a single sensor surface and a single optical system,although it should be realized that a plurality of sensor surfaces and aplurality of optical systems may be used, as also further describedbelow. Also, the terms “a sensor surface” and “at least one sensorsurface” as well as the terms “an optical system” and “at least oneoptical system” may be used interchangeably.

The sensor surface may be internally moved behind the optical system,such that an image plane defined by the optical system may be scanned bythe sensor surface. This implies that a static scene may be imaged withhigh accuracy, as the image may be acquired with a spectral resolutionby different rows of photo-sensitive areas of the sensor surfaceacquiring different wavelengths of light and the sensor surface is movedsuch that spectrally resolved information may be assigned to spatialpositions on the object. There is no need for the object to be moved inrelation to the optical system in order to acquire the image with highaccuracy.

Further, the example embodiments enable acquiring of an image using acompact imaging set-up. There is no need for complex components in theoptical system and the optical system does not need to be changed duringacquiring of an image. For instance, there is no need to use e.g.gratings for spectrally resolving received light and which may need tobe movable for directing light of a specific wavelength to differentrows of the photo-sensitive areas.

Also, thanks to the sensor surface being moved in relation to theoptical system, light of different wavelengths may be acquired with aconstant relationship between the object and an image plane. Thisimplies that no imaging artefacts may be introduced by changes to theoptical system. Further, imaging artefacts at edges of the opticalsystem may also be avoided.

It should be realized that the acquiring of a frame and moving of the atleast one sensor surface need to be alternately performed. On thecontrary, moving of the at least one sensor surface may be continuouslyperformed during a time period in which a plurality of frames areacquired. For instance, the acquiring of a frame may be triggered at atime when the continuously moved at least one sensor surface is in adesired position. If an exposure time used in acquiring a frame isrelatively short compared to a speed of movement of the at least onesensor, the acquired frame will not be affected by a movement blur.However, the acquiring and moving may alternatively be alternatelyperformed in a repetitive manner, wherein the moving of the at least onesensor surface is temporarily stopped during acquiring of a frame.

Each row of photo-sensitive areas on the sensor surface may be arrangedto detect light of a pre-selected range of wavelengths of light. Thus,all photo-sensitive areas in a row may be arranged to receive the samepre-selected range of wavelengths of light.

The pre-selected range of wavelengths of light may be different amongeach row of photo-sensitive areas. Thus, each row of photo-sensitiveareas may provide specific spectral information in the acquired imagesuch that the number of channels of the image equals the number of rowson the sensor surface.

A total movement of the sensor surface between a first frame and a lastframe to be included may be at least equal to a combined size of theplurality of rows of photo-sensitive areas of the sensor surface. Thisimplies that the sensor surface may be moved in relation to the opticalsystem, such that each channel of the image may provide informationrelating to the same two-dimensional part of the object. A magnitude ofthe total movement may be dependent on the number of rows per wavelengthband and a size of the acquired frames.

According to an embodiment, rows of photo-sensitive areas are arrangedin wavelength bands, each wavelength band comprising a plurality of rowsarranged to receive same wavelengths of light. The rows in a wavelengthband may further be arranged to receive different pre-selectedwavelengths, such that the number of channels of an acquired imageequals the number of wavelength bands on the sensor surface.

According to an embodiment of the method, moving the at least one sensorsurface comprises translating the at least one sensor surface a distancecorresponding to a height of the wavelength band. This implies that thewavelength band will image adjacent positions on the object in twosubsequent frames. Hence, each channel may be formed based on as fewframes as possible.

According to another embodiment, moving the at least one sensor surfacecomprises translating the at least one sensor surface a distancecorresponding to a height of an integer number of photo-sensitive areas,wherein the integer number is less than a number of rows in thewavelength band. Thus, the same position on the object may be imagedonto the same wavelength band in subsequent frames. This provides apossibility to selectively use information from several frames in orderto improve spectral information for a spatial position on the object.

According to an embodiment, a spatial position in a channel is based oninformation for a single wavelength band acquired in more than oneframe. For instance, an average of the detected incident light in theplurality of frames may be used. However, other combinations arepossible, such as using a median value, minimum value, maximum value ora percentile value.

According to an embodiment, the combining of information from theplurality of frames disregards information obtained at edge rows in thewavelength band. Pixels at an edge of a wavelength band may suffer fromcross-talk with an adjacent wavelength band. Thus, by disregarding edgerows, the risk of cross-talk between wavelength bands may be avoided.

According to an embodiment, the object is static during acquiring of theplurality of frames. Thanks to the object being static, the object isimaged in the same way onto the image plane during acquiring of theplurality of frames and, even though the frames are not acquired in thesame instant of time, there is no motion blur in the image.

According to another embodiment, the method further comprises moving acamera comprising the at least one optical system and the at least onesensor surface in concert with a movement of the object such that arelation between the object and the at least one optical system isstatic during acquiring of the plurality of frames. This implies thatthe object, even though it is moving, may still be imaged in the sameway onto the image plane during acquiring of the plurality of frames.

According to an embodiment of the device, the device may comprise acontrol unit for synchronizing movement of the at least one sensorsurface with acquiring of the plurality of frames. The control unit maybe arranged to alternate movement of the at least one sensor surfacewith acquiring of a frame. Alternatively, the control unit may bearranged to move the at least one sensor surface with a constant speedand synchronize acquiring of frames with the at least one sensor surfacebeing moved a distance corresponding to a height of an integer number ofpixels.

The control unit may be embedded into the device and may e.g. beimplemented in a processing unit of the device. However, according to analternative, the control unit may be external to the device. In suchcase, the device may comprise a receiver, which is arranged to receiveand forward control signals for synchronizing movement of the sensorsurface with acquiring of the plurality of frames.

According to an embodiment, the device further comprises a communicationunit for transmitting information in acquired frames to an externalunit. Thus, the acquired frames may be transmitted to an external unit,which may combine the acquired frames into an image havingtwo-dimensional spatial resolution and spectral resolution. This impliesthat the device need not include a processing unit for enabling thecombining, which may be beneficial if e.g. size requirements on thedevice are very harsh. This could for instance be the case if the deviceis to be used for endoscopic imaging.

According to another embodiment, the device further comprises acombining unit for combining information from a plurality of frames toform multiple channels of an image, wherein each channel is formed basedon detected light in respective rows of photo-sensitive areas andrepresents a two-dimensional image of the object for a differentwavelength. This implies that the device may be compact and that theimage may be formed within the device, so that there is no necessity toconnect the device to other components for forming the image.

According to an embodiment, the device further comprises at least onefilter which is arranged in relation to the at least one sensor surfacefor defining wavelength bands, each wavelength band comprising aplurality of rows of photo-sensitive areas arranged to receive samewavelengths of light. The filter may ensure that the desired wavelengthsare received by the respective rows of photo-sensitive areas. Further,using a filter may ensure that a row of photo-sensitive areas receivesthe same wavelengths in each acquired frame.

According to an embodiment, a number of the plurality of rows isdifferent for different wavelength bands. This implies that channelsrepresenting different wavelength bands may be acquired using differentset-ups. For instance, this may be used to adjust a signal-to-noiseratio depending on a quantum efficiency of the sensor and a filterresponse. Also, this may be used to give different weight to differentwavelength bands, e.g. based on expected different amounts of incidentlight in different wavelengths.

According to an embodiment, a set of adjacent wavelength bands define aspectral range of an image, and wherein the at least one sensor surfacecomprises a plurality of sets of wavelength bands repeated on the atleast one sensor surface. This implies that each wavelength band withina set of wavelength bands may be arranged to include fewer rows. Thus,the sensor surface may need to be translated a shorter distance in orderto obtain information of a full spectral resolution. Further, when acurrent image is being acquired, frames may include information ofwavelength bands of a subsequent image, such that information for asubsequent image may be acquired simultaneously with the current image.

According to an embodiment, the sub-set of the rows of photo-sensitiveareas for acquiring a frame are arranged in a position in the imageplane co-centric with an image circle defined by the optical system. Theoptical system may image an object onto an image circle and positionsbeing imaged closest to a center position of the image circle may beleast affected by any edge artefacts in the optical system. By thesub-set of rows on the sensor surface that are used in acquiring a framebeing arranged in a position defined co-centric with the image circle,it is ensured that the acquired information in each frame has no orlimited imaging artefacts from the optical system.

According to an embodiment, the device comprises a plurality of sensorsurfaces, wherein the plurality of sensor surfaces are arranged in acommon sensor plane and the translator is arranged to carry the commonsensor plane including the plurality of sensor surfaces. This impliesthat the device may comprise a plurality of sensor surfaces which mayeach be adapted for detection of specific range of wavelengths. Thus,the device may for instance comprise a first sensor surface adapted forultraviolet light, a second sensor surface adapted for visible andnear-infrared light, and a third sensor surface adapted for short-waveinfrared light. By scanning all these sensor surfaces over an imagecircle defined by an optical system, an object may be imaged with aspectral resolution spanning over a broad range of wavelengths. Thanksto the use of a plurality of sensor surfaces, each sensor surface may bespecifically adapted for detection of light within a specific range ofwavelengths.

According to an embodiment, the device comprises a plurality of opticalsystems, wherein each optical system in the plurality of optical systemsis arranged to define an image circle on an image plane and wherein theplurality of image circles are defined on a common image plane. Aplurality of optical systems may provide different opticalconfigurations (e.g. aperture, focal length, optical filters) such thata sensor surface when scanned over different image circles may obtaindifferent information. The plurality of optical systems may be arrangedin a relationship to each other, such that the image circles are definedon a common image plane, whereby the translator may be arranged to movethe at least one sensor surface in a planar movement for scanning the atleast one sensor surface over the plurality of image circles.

According to an embodiment, the at least one sensor surface is tilted inrelation to a direction of movement of the at least one sensor surfaceby the translator carrying the at least one sensor surface. This impliesthat different rows of photo-sensitive areas on a sensor surface will bearranged at different distances from the optical system when arranged inan image circle defined by the optical system. This could be used forhandling chromatic lens aberrations in the optical system, such that therespective rows of photo-sensitive areas will be arranged in a truefocal plane for the respective wavelength, when arranged in the imagecircle defined by the optical system.

According to an embodiment, the device is arranged to acquire a firstset of frames for forming a first image having two-dimensional spatialresolution and spectral resolution while moving the translator in afirst direction and acquire a second set of frames for forming a secondimage having two-dimensional spatial resolution and spectral resolutionwhile moving the translator in a second direction opposite to the firstdirection. This implies that the translator need not move the sensorsurface to an origin position after each scan in order to prepare foracquiring of a next image. Rather, images may be acquired as the sensorsurface is moved back and forth in relation to the optical system.Naturally, the information relating to specific wavelengths will beacquired in an opposite order when the translator is moved in the seconddirection compared to when the translator is moved in the firstdirection.

According to an embodiment, the device further comprises an illuminationsource, wherein the illumination source is controllable for controllinga spectral profile of illuminated light. A control unit may thus controlthe illumination source such that frames and/or images may be obtainedwith desired illumination.

According to an embodiment, the illumination source may be controlled tomatch wavelength bands being arranged in the image plane to receiveincident light from the optical system. Thus, the spectral profile ofthe illumination source may be varied during a scan of the rows ofphoto-sensitive areas over the image plane. The illumination source maythus e.g. match the quantum efficiency of each photo-sensitive area andthe spectral range of each photo-sensitive area.

According to another embodiment, the illumination source may becontrolled for respective images such that a specific image may beobtained under specific illumination. This implies that a plurality ofimages may be obtained under different illuminations providing differentinformation of an object to be imaged.

According to an embodiment, the translator is a piezo-electrictranslation stage for accurately moving the sensor surface. This impliesthat the translator may be implemented as a small component which mayaccurately control movement of the sensor surface.

BRIEF DESCRIPTION OF THE FIGURES

The above, as well as additional, features will be better understoodthrough the following illustrative and non-limiting detailed descriptionof example embodiments, with reference to the appended drawings.

FIG. 1 is a schematic drawing of a device, according to an exampleembodiment.

FIG. 2 is a schematic drawing illustrating movement of a sensor surface,according to an example embodiment.

FIG. 3 is a schematic drawing illustrating information acquired indifferent frames, according to an example embodiment.

FIG. 4 is a schematic drawing illustrating an image havingtwo-dimensional spatial resolution and spectral resolution being formedbased on the information acquired in the frames of FIG. 3.

FIG. 5 is a schematic drawing illustrating information acquired indifferent frames, according to an example embodiment.

FIG. 6 is a schematic drawing illustrating an image havingtwo-dimensional spatial resolution and spectral resolution being formedbased on the information acquired in the frames of FIG. 5.

FIG. 7 is a flow chart of a method, according to an example embodiment.

All the figures are schematic, not necessarily to scale, and generallyonly show parts which are necessary to elucidate example embodiments,wherein other parts may be omitted or merely suggested.

DETAILED DESCRIPTION

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawings. That which is encompassed by theclaims may, however, be embodied in many different forms and should notbe construed as limited to the embodiments set forth herein; rather,these embodiments are provided by way of example. Furthermore, likenumbers refer to the same or similar elements or components throughout.

The present disclosure will now be described more fully hereinafter withreference to the accompanying drawings, in which example embodiments areshown. This disclosure may, however, be embodied in many different formsand should not be construed as limited to the embodiments set forthherein; rather, these embodiments are provided for thoroughness andcompleteness, and fully convey the scope of the disclosure to theskilled person.

Referring now to FIG. 1, a device 100 for acquiring an image havingtwo-dimensional spatial resolution and spectral resolution will bedescribed. The device 100 comprises an optical system 102, which isconfigured to image an object towards an image plane 104 forming animage circle in the image plane 104.

The optical system 102 may comprise a number of optical components forproperly imaging the object, such as apertures, stops, and lenses. Theoptical system 102 may be adaptable to vary e.g. focus or magnificationof the optical system 102.

The device 100 further comprises a sensor surface 110, which may bearranged in the image plane 104 of the optical system. Thus, the opticalsystem 102 may be arranged to direct light from an object towards thesensor surface 110 in the image plane 104.

The device 100 may comprise a plurality of optical systems 102, whichmay be arranged side-by-side to each form an image circle in a commonimage plane 104. The optical systems 102 may each have differentconfigurations enabling imaging of an object with different opticalset-ups.

As will be further described below, the sensor surface 110 may bemovable in the image plane 104. When the device 100 comprises aplurality of optical systems 102, the sensor surface 110 may be movablein the common image plane 104 of the plurality of optical systems 102,such that the sensor surface 110 may in different frames record lightthat has passed different optical systems 102 and optical set-ups.

The device 100 may further comprise a plurality of sensor surfaces 110,which may be arranged in a common sensor plane. Each sensor surface 110may be adapted for detection of a specific range of wavelengths, e.g.ultraviolet, visible or infrared light. The plurality of sensor surfaces110 may thus enable acquiring light over a very broad range ofwavelengths, which may be useful for imaging an object with a spectralresolution spanning the broad range of wavelengths.

The plurality of sensor surfaces 110 may be used in combination with aplurality of optical systems 102, such that an object may be imaged withdifferent optical set-ups, while acquiring light over a very broad rangeof wavelengths.

Although the device 100 may comprise a plurality of optical systems 102and a plurality of sensor surfaces 110, for simplicity and brevity thedevice 100 will mainly be described below with reference to a singleoptical system 102 and a single sensor surface 110. Unless specificallystated below, the features described will also apply to a device 100comprising a plurality of optical systems 102 and/or a plurality ofsensor surfaces 110.

The device 100 may optionally comprise a light source 150 forilluminating the object, in order to provide desired lighting conditionswhen acquiring an image. The light source 150 may be arranged to provideillumination of specific wavelengths in order for the light to interactwith the object, such as being specularly or diffusely reflected orinducing emission of light, such as through fluorescence. The sensorsurface 110 may thus be arranged to receive and detect light from theobject.

The sensor surface 110 may comprise photo-sensitive areas 112, which maybe arranged in columns and rows. The sensor surface 110 may comprise acomplementary metal-oxide-semiconductor (CMOS) circuitry for arrangingphoto-sensitive areas 112 on the surface 110 and circuitry forcontrolling read-out of detection of light in the photo-sensitive area112. The photo-sensitive areas 112 may also be referred to as pixels.

The photo-sensitive areas 112 and the circuitry on the sensor surface110 may together form an image sensor for acquiring frames of imageinformation. Each frame may comprise information of detected incidentlight in at least a sub-set of rows of photo-sensitive areas 112. Theimage sensor may further be arranged to acquire a plurality of frames,wherein the plurality of frames may be combined to represent atwo-dimensional image of the object having a spectral resolution, aswill be described later.

A filter 114 may be integrated on the sensor surface 110. The filter 114may be arranged to pass specific wavelengths to rows of photo-sensitiveareas 112. Thus, the photo-sensitive areas 112 in a row may all bearranged to detect the same wavelengths of light. Further, rows ofphoto-sensitive areas may be arranged in wavelength bands such that aplurality of rows receives the same wavelengths of light, whereasdifferent wavelength bands receive different wavelengths.

Each wavelength band may define a narrow range of wavelengths which aredetected by the photo-sensitive areas 112 in the wavelength band. Thewavelength bands may be a plurality of adjacent wavelength bands in arange of wavelengths. However, according to an alternative, thewavelength bands may be a plurality of selected wavelength bands from arange of wavelengths, wherein the wavelength bands are not necessarilyadjacent to each other in the wavelength spectrum.

Each wavelength band may define a different, pre-selected wavelengthinterval, which is detected by the photo-sensitive areas 112 in thewavelength band. The wavelength bands may be adapted to specificrequirements, e.g. for facilitating analysis of an object for presenceof a compound. The wavelength bands may alternatively comprise a numberof adjacent wavelength intervals in a broad range of wavelengthsallowing acquiring a two-dimensional image of an object with a spectralresolution facilitating general use of the spectral information.

The sensor surface 110 may be mounted on a translator 120. Thetranslator 120 may thus carry the sensor surface 110 and may accuratelycontrol placement of the sensor surface 110 in the image plane 104. Thetranslator 120 may be arranged as a piezo-electric translation stage,which may be accurately controlled in order to provide an accurateplacement of the sensor surface 110 in the image plane 104. Thus, thesensor surface 110 may be moved in the image plane 104.

As mentioned above, the filter 114 may be integrated to the sensorsurface 110 such that the filter 114 will move with the sensor surface110 and the same row of photo-sensitive areas 112 will detect the samewavelengths of light regardless of the placement of the sensor surface110 in the image plane 104. Alternatively, the filter 114 may also bemounted on the translator 120 or connected to the sensor surface 110,such that the filter 114 will move with the sensor surface 110.

The device 100 may further comprise a control unit 130, which may bearranged to control the translator 120 and may further be arranged tocontrol the image sensor to acquire a frame. The control unit 130 maythus be arranged to synchronize movement of the sensor surface 110 andacquiring of frames, as will be further described below.

The control unit 130 may be implemented as a microprocessor, which maybe programmable for controlling operation of the microprocessor. Forinstance, the processing unit may be a central processing unit (CPU).The processing unit may alternatively be a special-purpose circuitry forproviding only specific logical operations. Thus, the processing unitmay be provided in the form of an application-specific integratedcircuit (ASIC), an application-specific instruction-set processor (ASIP)or a field-programmable gate array.

The device 100 may also comprise a combining unit 132 for combininginformation from a plurality of frames to form multiple channels of animage. The combining unit 132 may be implemented in the same processingunit as the control unit 130 or in another processing unit speciallyadapted to combining of frames.

It should be realized that one or more of the control unit 130 and thecombining unit 132 may alternatively be arranged in an external unit andneed not be part of the device 100. The device 100 may thus insteadcomprise an interface for receiving control signals from an externalunit and/or transmitting information in acquired frames to an externalunit.

The interface may comprise a communication unit 140 for transmittingand/or receiving information to and from an external unit. Thecommunication unit 140 may be arranged for wired or wirelesscommunication.

In some embodiments, a size of the device 100 may be critical, e.g. ifthe device 100 is to be used for endoscopic imaging. In such case, thecontrol unit 130 and/or the combining unit 132 may alternatively bearranged in an external unit, such as a personal computer connected tothe device 100 such that processing power is arranged externally to thedevice 100.

The device 100 may be formed in a single housing, such that a relationbetween the optical system 102 and the translator 120 iswell-controlled. This may also ensure that a compact assembly of thedevice 100 is provided.

Referring now to FIG. 2, movement of the sensor surface 110 andacquiring of frames will be further explained. FIG. 2 illustrates animage circle 200 projected by the optical system 102 onto the imageplane 104. The image circle is scanned by the sensor surface 110.

The sensor surface 110 is moved in a direction perpendicular to alongitudinal direction of the rows of photo-sensitive areas 112, asindicated by arrow A. A plurality of frames is acquired while the sensorsurface 110 is moved in the image plane 104. A row of photo-sensitiveareas 112 may thus detect incident light in a number of frames,detecting light from different parts of the object in each frame.

The plurality of frames may then be combined to form multiple channelsof an image. Each channel may be formed based on detected light in awavelength band and represent a two-dimensional image of the object forthe wavelengths detected in the wavelength band. Together the multiplechannels may form a hyperspectral cube, i.e. imaging the object in twospatial dimensions and in a third spectral dimension.

The sensor surface 110 may be tilted in relation to a direction ofmovement of the sensor surface 110. Hence, a non-zero angle may beformed between a longitudinal direction of columns of the sensor surface110 and the movement direction A. This implies that different rows ofthe sensor surface 110 may be arranged at different distances to theoptical system 102 and may allow for diminishing errors e.g. due tochromatic aberrations of the optical system 102, which may cause thetrue image plane 104 to be at different distances from the opticalsystem 102 for different wavelengths of light.

The optical system 102 may also or alternatively be dynamicallycontrolled such that the optical system 102 may be adapted to thewavelengths of light to be recorded in a specific frame in order todiminish errors due to e.g. chromatic aberrations.

As indicated in FIG. 2, a first frame, frame 0, is acquired when thesensor surface 110 is mostly outside the image circle. In FIG. 2, only asingle row of photo-sensitive areas 112, namely the row 116 a leadingthe movement of the sensor surface 110 in the scanning direction A,receives light. Then, the sensor surface 110 is moved in the scanningdirection A so that the row 116 a in sequential frames receives lightfrom different parts of the object. The sensor surface 110 is thengradually moved out of the image circle again until a last frame, frameN, is acquired when the sensor surface 110 is mostly outside the imagecircle again. In the last frame, only the row 116 b trailing themovement in the scanning direction A receives light.

Depending on the optical system 102 and sensor dimensions, a size of thescanned area may vary. However, to obtain a hyperspectral cube of a sizeof the sensor itself, two times the number of wavelength bands minus oneframes need to be acquired, as illustrated in FIG. 2.

As explained above, the device 100 may comprise a plurality of sensorsurfaces 110. The plurality of sensor surfaces 110 may thus sequentiallyscan the image circle, whereby the object may be imaged by the opticalsystem 102 onto a plurality of sensor surfaces 110 for recordingdifferent ranges of wavelengths. The recorded frames from the pluralityof sensor surfaces 110 may be combined into a large hyperspectral cubespanning a very broad range of wavelengths.

Also, the device 110 may comprise a plurality of optical systems 102.The optical systems 102 may image slightly different parts of an object,e.g. with different optical set-ups. A separate image in the form of ahyperspectral cube may be formed based on each optical system 102.

If the object is moved in relation to the optical systems 102, the samepart of the object may be imaged by the plurality of optical systems 102in sequential imaging sequences.

The plurality of optical systems 102 may be used for imaging in anobject with different configurations, varying e.g. apertures, focallength and/or optical filters.

Differences in apertures between the optical systems enable for instancethe implementation of a High Dynamic Range image reconstruction.Differences in focal length between the optical systems enable scanningwith different magnifications and field of views, as e.g., in amicroscopy setup. Different optical filters between the optical systemsenable enhancing the spectral quality by avoiding for instance spectralmixing in bands with multiple peaks. The different optical filters wouldalso be needed when scanning with multiple sensor surfaces in differentspectral ranges. A plurality of optical systems with different opticalaxes may enable (multi-) stereo 3D hyperspectral imaging.

The plurality of frames (acquired in relation to a single optical system102) should be acquired while the object is static, such that motionblur is not introduced into the image.

According to an alternative embodiment, the device 100 is arranged tomove in concert with the object, e.g. along a conveyor belt, such thatthe object appears static in relation to the optical system 102. Thus,the plurality of frames while a same position on the object is imagedonto a same position in the image plane 104, such that no motion blurwill be introduced in the acquiring of a plurality of frames.

The device 100 may be used in a start/stop mode, where translation ofthe sensor surface 110 is halted between frames. Thus, no motion of thesensor surface 110 occurs during acquiring of a single frame and anymotion blur may thus be avoided.

However, the device 100 may alternatively be used in a continuous mode.The frames may thus be acquired when the sensor surface 110 is atspecific positions in the image plane 104 by providing triggering of theacquiring of a frame in synchronization with a speed of movement of thesensor surface 110. The translator 120 may move the sensor surface 110with such precision that sub-pixel registration of the frames may beallowed. The speed of movement of the sensor surface 110 may be so lowthat the sensor surface 110 is not moved a distance longer than a heightof a wavelength band during acquisition time. Pixel blur (i.e. adisplacement in number of pixels of the sensor surface 110 occurringduring image acquisition) may be controlled and the resulting image canbe binned to reduce noise.

In either of the above modes movement of the translator 120 needs to beaccurately controlled, such that a position of a row of photo-sensitiveareas 112 of the sensor surface 110 in the imaging plane 104 isaccurately known. In the start/stop mode, the translator 120 may bearranged to move the sensor surface 110 a distance corresponding to aheight of an integer number of photo-sensitive areas 112, e.g.corresponding to a size of a wavelength band.

The light source 150 may further be controlled, e.g. by the control unit130, such that a spectral profile (e.g. a specific wavelength of light)of the emitted light may match a sensitivity of the rows 116 of thesensor surface 110 which are arranged in the image circle.

By the light source 150 being controlled by the control unit 130,synchronization of the emitted light with the movement of the sensorsurface 110 may be facilitated. However, it should be realized that thelight source 150 may be controlled by a separate controller, e.g.embedded in the light source 150.

In one embodiment, the light source 150 may be controlled to change thespectral profile at each frame to be acquired. The light source 150 maythus be tuned to specifically match a quantum efficiency and spectralrange of each wavelength band that passes the image circle.Alternatively, the light source 150 may be controlled to change thespectral profile one or a few times during scanning of the sensorsurface 110 over the image circle to adjust to a continuous change ofsensitivity of the wavelength bands in the image circle.

In one embodiment, the light source 150 may be controlled to change inrelation to different sensor surfaces 110 being arranged in the imagecircle. For instance, if a first sensor surface 110 is arranged todetect ultraviolet light and a second sensor surface 110 is arranged todetect visible light, the light source 150 may be controlled to emitultraviolet light when the first sensor surface 110 is in the imagecircle and to emit visible light when the second sensor surface 110 isin the image circle.

In another embodiment, the light source 150 may be controlled to changethe illumination for different passes of the sensor surface 110 over theimage circle. For instance, a broadband visible light illumination mayfirst be used in a first scan of the sensor surface 110 over the imagecircle. Then, an illumination for inducing fluorescence may be used in asecond scan allowing acquiring a first image of an object in visiblelight and a second fluorescence image of the object. This may be veryuseful in some applications, such as fluorescence guided surgery, wherefluorescence localization algorithms require intrinsic measurements (atthe excitation wavelength) and fluorescence measurements.

Referring now to FIGS. 3-6, two examples of movement of the sensorsurface 110 and the combination of frames into an image having spectralresolution will be given. The movement between subsequent frames iscalled a step-size and is quantified as the number of pixels to whichthe movement corresponds.

In a first example, illustrated in FIGS. 3-4, the sensor surface 110comprises 4 wavelength bands, each comprising 4 rows of pixels. Thesensor surface 110 is moved using a 4 pixel step between frames. In thiscase, 7 frames are acquired in order to complete a data set for formingfour channels each representing a two-dimensional image of the objectfor a specific wavelength band.

It is clear from FIG. 3 that only pixel positions 13-28 contain allspectral bands and a combined image may thus be formed, as illustratedin FIG. 4, for these pixel positions. The combined image comprisesspectral information of four different wavelength bands for everyspatial position in the image and the combined image is as large as thesize of the image sensor.

In the example of FIGS. 5-6, the sensor surface 110 comprises 3wavelength bands, each comprising 8 rows of pixels. The sensor surface110 is moved using a 3 pixel step between frames. Here, 14 frames areacquired as illustrated in FIG. 5.

Since each wavelength band comprises 8 rows of pixels, and a 3 pixelstep is used, a spatial position of the object is imaged in a singlewavelength band in a plurality of frames. This allows pixels at the edgeof each band to be discarded, in order to avoid cross-talk betweenadjacent wavelength bands. Further, information relating to each spatialposition is still acquired in two frames for each wavelength band.Information from a plurality of frames may be combined in severaldifferent ways. For instance, an average of the detected incident lightin the plurality of frames may be used. Alternatively, a median value, aminimum value, a maximum value or a percentile value may be used.

It should be realized that the above examples described in relation toFIGS. 3-6 are given in order to facilitate explanation of how aplurality of frames may be acquired and are related to each other. Inpractical examples, the size of the sensor surface 110 is larger and alarger number of wavelength bands may be used.

In one embodiment, a sensor surface 110 comprises 128 wavelength bandsof 8 pixels each (1024 pixel rows) by 2048 columns. The device 100 maythen be arranged to acquire 255 frames using an 8 pixel step. Each pixelmay have a height of 5.5 μm, which implies that the sensor surface willin total be moved 11.22 mm. The sensor can be operated at acquiring 350frames per second, such that a full hyperspectral cube (1024×2048pixels×128 wavelength bands) may be acquired in 0.72 seconds. Thus, thefull hyperspectral cube may be quickly obtained, which does not set verylimiting requirements on having a static object in relation to theoptical system 102.

The wavelength bands on the sensor surface 110 may be designed withdifferent widths (different number of rows per wavelength band). Thismay be used for adjusting a signal-to-noise ratio depending on quantumefficiency of the photo-sensitive areas 112 and filter response.

A set of adjacent wavelength bands define a spectral range that may beacquired by the sensor surface 110. According to an embodiment, thesensor surface 110 comprises a plurality of sets of wavelength bandsrepeated on the sensor surface 110.

For instance, a sensor surface 110 may have 128 different wavelengthbands, each covering 8 rows of the sensor surface 110. By repeating thesets of wavelength bands on a same-size sensor surface 110, the sensorsurface 110 may instead have two times the same 128 bands each covering4 rows of the sensor surface 110. Then, in order to acquire an imagespectrally resolved over the 128 band, it is only necessary to move thesensor surface 110 half the distance. Thus, a rate of acquired imagesmay be increased, in particular if the sensor surface 110 is moved incontinuous mode.

Further, since the wavelength bands are repeated on the sensor surface110, acquiring of a subsequent image may be initiated while a currentimage is acquired. For instance, with reference to FIG. 3, while frames5-7 are acquired for a current image, frames 1-3 for the subsequentimage may be acquired. This implies that the subsequent image may beacquired quickly after the acquiring of the current image.

According to an embodiment, an image may be acquired when the sensorsurface 110 is moved in a first direction over the image circle. Oncethe entire sensor surface 110 has been scanned, another image may beacquired while the sensor surface 110 is moved back over the imagecircle in a second direction opposite the first direction. Thus, imagesmay be acquired as the translator 120 moves the sensor surface 110 backand forth over the image circle. The wavelength band leading themovement of the sensor surface 110 in the first direction will betrailing the movement of the sensor surface 110 in the second direction.This implies that an order of acquiring information relating todifferent wavelength bands will be changed between the first and seconddirection. However, this may be easily handled when combining framesinto an image having spectral resolution.

Using a plurality of sets of wavelength bands repeated on the sensorsurface 110 and acquiring images when moving the translator 120 in boththe first direction and the opposite second direction may be used foracquiring images having a full spectral resolution at a very high rate.This may be used in order to acquire video-type imaging of an object ora scene with a high spectral resolution. For instance, using a sensorsurface 110 having 64 wavelength bands, each of one row, repeated 8times on the sensor surface 110, and scanning back and forth may resultin a rate of about 10 images per second.

Referring now to FIG. 7, a method 300 for acquiring an image will bedescribed. The method comprises acquiring, step 302, a frame using rowsof photo-sensitive areas 112 on a sensor surface 110. The method furthercomprises moving, step 304, the sensor surface 110 in the image plane104 in a direction perpendicular to a longitudinal direction of the rowsof photo-sensitive areas 112. The acquiring 302 of a frame is repeatedfor acquiring a plurality of frames, wherein the sensor surface 110 isdifferently arranged to the optical system 102 for different frames.Thus, different spectral information for respective positions on theobject is recorded based on the sensor surface 110 in different frames.

Then, information from the thus-acquired plurality of frames arecombined, step 306, to form multiple channels of an image, wherein eachchannel is formed based on detected light in respective rows ofphoto-sensitive areas 112 and represent a two-dimensional image of theobject for a different wavelength interval.

Optionally, before initiating combining of a plurality of frames, acheck may be performed whether the sensor surface 110 has been scannedover the entire surface to be scanned (e.g. over all wavelength bands),so that each spatial position of an object has been imaged onto eachwavelength band on the sensor surface 110. If not, the repeating of thestep 302 for acquiring a plurality of frames using different positionsof the sensor surface 110 in relation to the optical system 102 may becontinued in order to obtain further frames before combining of aplurality of frames is initiated.

If the check finds that the desired frames have been acquired, thecombining 306 of information from the thus-acquired plurality of framesmay be initiated.

It should be realized, however, that the step 306 of combining pluralityof frames to form multiple channels of an image may be initiated beforeall frames have been acquired. Also, an image may be formed even if allframes are, for some reason, not acquired. Hence, if the check neverfinds that the entire surface to be scanned has actually been scanned,the step 306 may still be performed based on the frames that have beenacquired to form an image which may lack information of some of themultiple channels.

In the above, the disclosure has mainly been described with reference toa limited number of embodiments. However, as is readily appreciated by aperson skilled in the art, other embodiments than the ones disclosedabove are equally possible within the scope of the disclosure, asdefined by the appended claims.

While some embodiments have been illustrated and described in detail inthe appended drawings and the foregoing description, such illustrationand description are to be considered illustrative and not restrictive.Other variations to the disclosed embodiments can be understood andeffected in practicing the claims, from a study of the drawings, thedisclosure, and the appended claims. The mere fact that certain measuresor features are recited in mutually different dependent claims does notindicate that a combination of these measures or features cannot beused. Any reference signs in the claims should not be construed aslimiting the scope.

What is claimed is:
 1. A camera for acquiring a hyperspectral imagehaving two-dimensional spatial resolution comprising: at least oneoptical system, wherein each optical system of the at least one opticalsystem is configured to define an image plane and direct light from anobject towards the image plane; at least one sensor surface comprisingphoto-sensitive areas for detecting incident light from one or moreparts of the object, wherein the photo-sensitive areas are arranged toreceive and detect the light from the object; at least one filtercomprising a filter response that defines a plurality of wavelengthbands, wherein the at least one filter is arranged in relation to the atleast one sensor surface such that each wavelength band spatiallycorresponds to one or more rows of photo-sensitive areas; a translator,wherein the translator is configured to move the at least one sensorsurface (i) in the image plane in a direction perpendicular to alongitudinal direction of the rows of photo-sensitive area and (ii) at adistance corresponding to a height of photo-sensitive areas spatiallycorresponding to a respective wavelength band; the translator beingconfigured for synchronized movement of the at least one sensor surfacewith acquiring of a plurality of frames, wherein a frame in theplurality of frames is acquired by arranging a sub-set of the rows ofphoto-sensitive areas in the image plane to receive incident light fromthe at least one optical system; and a combining unit for combininginformation from a plurality of frames to form multiple channels of animage and to represent a two-dimensional hyperspectral image of theobject, wherein each channel is formed based on detected light inrespective rows of photo-sensitive areas.
 2. The camera according toclaim 1, wherein a number of the one or more rows of photo-sensitiveareas spatially corresponding to a given wavelength band is differentfor different wavelength bands.
 3. The camera according to claim 1,wherein a set of adjacent wavelength bands define a spectral range of animage, and wherein the at least one sensor surface comprises a pluralityof sets of wavelength bands repeated on the at least one sensor surface.4. The camera according to claim 1, further comprising a plurality ofsensor surfaces, wherein the plurality of sensor surfaces are arrangedin a common sensor plane and the translator is arranged to carry thecommon sensor plane including the plurality of sensor surfaces.
 5. Thecamera according to claim 1, further comprising a plurality of opticalsystems, wherein each optical system in the plurality of optical systemsis configured to define an image circle on an image plane and wherein aplurality of image circles are defined on a common image plane.
 6. Thecamera according to claim 1, wherein the at least one sensor surface istilted in relation to a direction of movement of the at least one sensorsurface by the translator carrying the at least one sensor surface. 7.The camera according to claim 1, wherein the camera is arranged toacquire a first set of frames for forming a first image havingtwo-dimensional spatial resolution and first spectral information whilemoving the translator in a first direction and acquire a second set offrames for forming a second image having two-dimensional spatialresolution and second spectral information while moving the translatorin a second direction opposite to the first direction.
 8. The cameraaccording to claim 1, further comprising an illumination source, whereinthe illumination source is controllable for controlling a spectralprofile of illuminated light.
 9. The camera according to claim 1,wherein the translator is configured to move the at least one sensorsurface a distance corresponding to a height of an integer number ofphoto-sensitive areas, wherein the integer number of photo-sensitiveareas is less than a number of rows spatially corresponding to a givenwavelength band.